Pharmaceutical giant Pfizer is facing a growing lawsuit in the United States over claims that its contraceptive injection, Depo-Provera, caused brain tumours in women who used it long-term.

The class action, brought by law firm Levin Papantonio, alleges that Pfizer failed to warn women and doctors about the increased risk of intracranial meningioma if Depo-Provera is used for more than a year.

A court hearing is scheduled in Pensacola, Florida, on Monday.

Since May, the number of plaintiffs has tripled to more than 1,300 cases, consolidated into multi-district litigation. Lawyers expect the total to rise to between 5,000 and 10,000 claims, with potential damages reaching billions of dollars.

Scientific studies have raised concerns about the safety of Depo-Provera. Research published in the British Medical Journal in March 2024 found that prolonged use of certain progestogen medications was linked to a higher risk of intracranial meningioma, a type of benign brain tumour. Depo-Provera was specifically linked to a 5.6-fold higher risk.

While meningiomas are not usually cancerous, they can cause seizures, headaches, and loss of vision or hearing. Surgical removal is often necessary but carries risks of damaging surrounding brain structures.

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FDA and the debate over drug label warnings

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At the center of the Pfizer lawsuit is the question of whether the company acted responsibly in warning patients. Pfizer argues that it sought to add a tumour warning to Depo-Provera’s label, but the FDA rejected the request.

“This is a clear pre-emption case because FDA expressly barred Pfizer from adding a warning about meningioma risk, which plaintiffs say state law required,” the company said in court filings.

Plaintiffs counter that Pfizer’s request was too broad, grouping Depo-Provera with other lower-dose contraceptives, which led to the FDA’s decision. They argue the company failed to provide adequate data that might have justified a targeted warning.

Depo-Provera, marketed since the 1980s, is used by millions of women worldwide, both for contraception and to treat conditions such as endometriosis. Around 247 million women globally use hormonal contraceptives, and nearly a quarter of sexually active women in the United States have used Depo-Provera.

Warning labels were updated in the UK in 2024, and similar updates have been made in Canada and Europe. Pfizer has said it is “aware of this potential risk associated with long-term use of progestogens.”

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What the lawsuit could mean for Pfizer

Virginia Buchanan, co-chair of the plaintiffs’ executive committee, accused Pfizer of avoiding accountability: “Pfizer is attempting to avoid accountability by invoking a pre-emption defense, yet there are serious questions about whether it ever provided the FDA with the full picture."

Buchanan added, “Pre-emption was never meant to serve as a shield for drug companies that fail to warn patients adequately. Pfizer has consistently failed to take reasonable steps to alert patients and their physicians to this very real danger.”

In addition to the class action, law firm Berger Montague is investigating whether Pfizer’s board breached its fiduciary duties in the marketing and sale of Depo-Provera, which could lead to shareholder lawsuits.

With thousands of potential plaintiffs and billions of dollars at stake, the Pfizer lawsuit could become one of the most consequential pharmaceutical cases in recent years.